The magnitude of response of a target cell to any sex hormone depends not only upon the amount of hormone available to that cell but also upon the amount of hormone receptor present within the cell. Biochemical evidence indicates that hormone receptor levels are labile, being modulated by various factors present within the hormonal milieu. While biochemical techniques have documented the hormone-induced changes in hormone receptor levels, they are not sensitive enough to distinguish these levels in the individual cell types comprising heterogeneous target cell populations. This fact becomes important since our autoradiographic data show that each cell type within the anterior pituitary contains a different amount of estradiol receptor and responds differently to various hormonal manipulations. Consequently, each subpopulation of cells must be considered as a separate, independent entity when studying the response of a target tissue to a hormone. Initially, androgen, estrogen and progestogen nuclear receptor levels will be measured in pituitary gonadotropes, lactotropes, thyrotropes and somatotropes and in several target cell populations of the brain and peripheral tissues in intact male and female rats. Statistically analyzed silver grain counts from autoradiograms made by the dry-autoradiographic and the dry-autoradiographic - immunocytochemical method will be used to compare receptor levels in nuclei of different cell populations. Next, the effects of selective hormone deprivation upon these sex hormone receptor levels will be measured in castrated, adrenalectomized and thyroidectomized male and female rats. Finally, the effects of specific sex steroid, hypophyseal and hypophyseotrophic hormones upon estradiol receptor levels will be quantitatively analyzed.